A cohort of anti-HIV positive donors and controls has been under prospective follow-up since 1985. The original analysis of the study was published in the New England Journal of Medicine (321:917, 1989). The cohort is now in its 12th year of follow-up. At enrollment, 182 subjects were Western blot (WB) positive, including 158 asymptomatic donors, 9 sexual partners of these donors, and 15 persons infected by blood transfusion. In addition, we enrolled a control population consisting of 70 donors who were anti-HIV reactive on the screening enzyme immunoassay (EIA), but WB negative or WB indeterminate (21). Of the 182 participants who were Western blot positive, 87% were donors, 5% sexual partners, and 8% recipients. Of the 182 WB positives, 56 (31%) are alive and in active follow-up; 57 (31%) are dead, of whom 53 (93%) died of AIDS; and 71 (39%) are lost to follow-up (LTFU). We suspect that most LTFU have succumbed to AIDS, but we need access to the National Death Index to establish this: 11 of the 71 LTFU were known to have AIDS at the time they left the study. Of the 56 patients who are in active follow-up, 42 (75%) are males. Fifty- one (91%) were detected at the time of blood donation, 1 was a blood recipient, and 4 are sexual partners of index donors. Twenty of 56 (36%) have had an AIDS-defining event. Others have CD4 counts under 300, but have had a stable course even before treatment. A subset of 14 patients have exceeded 10 years of follow-up and have CD4 counts persistently >400 with no AIDS defining infections and no physical abnormalities except minor adenopathy. Our goal will be to focus on this group in terms of predictive factors for long-term non-progression. AIDS or HIV-related phenomena have not developed in any of the 21 WB indeterminate or 70 WB negative subjects.